The cyclosporins comprise a class of structurally distinctive, cyclic, poly-N-methylated undecapeptides, commonly possessing pharmacological, in particular immunosuppressive, anti-inflammatory and antiparasitic activity. The first of the cyclosporins to be isolated was the naturally occurring fungal metabolite Ciclosporin or Cyclosporin, also known as cyclosporin A.

Since the original discovery of Cyclosporin, a wide variety of naturally occurring cyclosporins have been isolated and identified, and many further non-natural cyclosporins have been prepared by total- or semi-synthetic means or by the application of modified culture techniques. The class comprised by the cyclosporins is thus now substantial and includes, for example, the naturally occurring cyclosporins A through Z [cf., Traber et al.; 1, Helv. Chim. Acta, 60, 1247-1255 (1977); Traber et al.; 2, Helv. Chim. Acta, 65, 1655-1667 (1982); Kobel et al.; Europ. J. Applied Microbiology and Biotechnology, 14, 273-240 (1982); and von Wartburg et al.; Progress in Allergy, 38, 28-45 (1986)], as well as various non-natural cyclosporin derivatives and artificial or synthetic cyclosporin derivatives and artificial or synthetic cyclosporins including dihydrocyclosporins [in which the -MeBmt-residue is saturated by hydrogenation]; derivatized cyclosporins (e.g., in which the 3′-O-atom of the -MeBmt-residue is acylated or a further substituent is introduced at the α-carbon atom of the sarcosyl residue at the 3-position); and cyclosporins in which variant amino acids are incorporated at specific positions within the peptide sequence, e.g. employing the total synthetic method for the production of cyclosporins developed by R. Wenger—see e.g. Traber et al., 1; Traber et al., 2; and Kobel et al., loc cit. U.S. Pat. Nos. 4,108,985, 4,220,641, 4,288,431, 4,554,351, 4,396,542 and 4,798,823; European Patent Publication Nos. 34,567A, 56,782A, 300,784A and 300,785; International Patent Publication No. WO 86/02080 and UK Patent Publication Nos. 2,206,119 and 2,207,678; Wenger 1, Transpl. Proc., 15 Suppl. 1:2230 (1983); Wenger 2, Angew. Chem. Int. Ed. 24 77 (1985) and Wenger 3, Progress in the Chemistry of Organic Natural Products, 50, 123 (1986).
Several synthetic modifications of the -MeBmt-residue residing at position 1 of the cyclosporin undecapeptide have been described including: Park et al., Tetrahedron Lett. 1989, 30, 4215-4218; U.S. Pat. Nos. 5,239,037, 5,293,057; U.S. Publication Nos. US20020142946, US20030087813, and US20030104992 assigned to Enanta Pharmaceuticals, Inc.; PCT Publication Nos. WO99/18120 and WO03/033526 both assigned to Isotechnika; and U.S. Pat. Nos. 4,384,996, 4,771,122, 5,284,826, and 5,525,590 assigned to Sandoz.
The compound cyclosporine (cyclosporine A or CsA) has found wide use since its introduction in the fields of organ transplantation and immunomodulation, and has brought about a significant increase in the success rate for transplantation procedures. Undesired side effects associated with cyclosporine, however, such as nephrotoxicity, have led to a continued search for immunosuppressant compounds having improved, efficacy and safety.
Side effects with systemic CsA include increase in diastolic blood pressure and decrease in renal function. Other side effects include hepatic dysfunction, hypertrichosis, tremor, gingival hyperplasis and paraesthsia. The systemic toxicity of CsA limits its use for the treatment of certain diseases. Accordingly, a need exists for compounds which exhibit immunosuppressive activity while not producing systemic toxicity.